Chemical fertilisers in agriculture—help or harm?

Science fiction writers delight in bringing us mutant creatures, born of the incessant human desire to tinker with nature. Considering their application as plant nourishers, it’s surprising no-one has yet come up with a story about chemical fertilisers spawning giant, carnivorous plants.

It’s easy to dismiss the mole people, sharktopusses and giant crab-monsters as pure fantasy. Until you consider the fact that 3D printing, i-pads, credit cards, submarines and flat-screen TVs all featured in science fiction well before they became science fact.

These ideas were all considered crazy in their time too. But now, they’re part of our everyday lives. Of course, we’re not claiming chemical fertilisers are really at risk of creating man-eating plant-creatures. But it is worth investigating just how helpful and harmful they actually are.

Inorganic vs organic fertilisers

The difference between the two is all in how they’re made. Generally, if a scientist was involved, it’s probably a chemical fertiliser. If it grew naturally, or something pooped it out, it’s organic.

Common chemical fertilisers

Nitrogen fertilisers, made from ammonia;

Phosphate fertilisers, extracted from minerals;

Potassium fertilisers, purified from salt crystals;

Compound fertilisers, combo of the above chemicals.

Common organic fertilisers

Animal waste, like cow, chicken and horse manure;

Plant matter;

Organic soils, like peat;

Human waste (one of the oldest but most controversial forms of organic fertilisation).

How much synthetic fertiliser are we actually using?

According to statistics from the World Bank, chemical fertiliser use is on the rise all over the world. Australia is no different. While there have been a few minor dips, the general trend is onward and upward, with more and more chemicals used each year.

Chemical fertilisers: the good

Humans have been putting poop on plants for aeons. With great results. But, then something interesting happened in the mid 20th century. An agricultural revolution and scientific boom occurred in unison. Inevitably, the two fields met and science dove in, with great minds applying their knowledge to improving every aspect of the farming industry.

Chemical fertilisers are one of many innovations to come out of that time. If used wisely, they give farmers greater control over their crops. You are able to combine certain fertilisers and deliver precise concentrations to the plants to improve yields and soil quality and even ward off some pests. Sounds great in theory, right? But, if we’ve learned anything from Chernobyl, super-bugs, cane toads and flat earth theorists it’s this: science doesn’t always get it right.

When good fertilisers go bad

For a long time, fertilisers weren’t even covered by the national agvet registration scheme and so didn’t undergo the same level of monitoring as pesticides, despite their chemical nature. While their use is now controlled, they are still something of an unknown quantity.

Some chemical fertilisers have a short life-cycle, requiring constant re-application. This adds to costs for the farmer and increases the affects on the environment. According to an in-depth study published by the Australian Academy of Technological Sciences and Engineering,

“Fertilisation can result in relatively abrupt changes in soil pH and consequently affect the behaviour of some pesticides adsorbed to soils.”

What does this mean? Who knows. We do know chemical fertilisers interact with other products, like pesticides, but we don’t know precisely how and if those interactions are harmless, bad for your soil and plants, dangerous for you or catastrophic for the environment (lets not forget, they thought cane toads were a koota idea at one point).

Because the chemicals are not in their naturally occurring state, the plants are often not able to absorb them completely. The result? Potentially harmful nitrate residue leaching into soil and waterways. Traces of synthetic fertilisers have been found in rivers, creeks and lakes all over the world. How much damage these chemicals are doing is still being looked into. However, scientists from publications like the New Zealand Journal of Marine and Freshwater Research, recommend caution and use of buffer strips to prevent run-off.

We have seen huge algae blooms forming in waterways as a result of fertiliser run-off. Like something out of a fifties science fiction movie, these beasty aquatic plants are sometimes big enough to block up waterways altogether and, when they die, their massive decomposing bodies suck oxygen from the water.

This turns the whole area into a no-go zone for fish and other water-dwelling creatures. Leaving them with the unappealing ultimatum of dying or fleeing to safer territory.

Chemical fertilisers: the verdict

To give you a real conclusion, we trawled through the latest academic research on the effects of inorganic vs organic fertilisers.

What we can tell you: cutting back on your use of chemical fertilisers will benefit you, your crops and the environment.

What we can’t tell you: the exact ratio that will be optimum for your farm or garden.

We found a general consensus that a blended approach works best for growth and yield. Most of the studies we looked at found a significant improvement through decreasing the use of chemical fertilisers; not cutting them out all together, just cutting them down.

The International Journal of Natural Sciences found optimal results with a 40% reduction in use of inorganic fertilisers. A report in Science of the Total Environment produced similar results, concluding the combination treatment works best when weighted towards organic fertilisers. Taking this approach, they found:

“improved soil water retention, nutrient status and nutrient uptake by plants due to the addition of organic treatments were accompanied with increased plant growth and yield.”

Because scientists can never agree, it is worth mentioning a report from the Crop and Weed Science Society that found optimal results with a 75:25 ratio of inorganic to organic fertilisers.